What is cancer of unknown primary?
Cancer of unknown primary (CUP) is the term used to describe a metastatic cancer (cancer that has spread) with an unknown starting point.
In Australia, CUP is the fifth most common cause of cancer death in men and fourth most common cause of cancer death in women.
Usually, when cancer spreads, the secondary cancer cells look like abnormal versions of the primary cancer cells (in the tissue where the cancer began). For example, if breast cancer spreads to the lungs, the metastatic tumour in the lung is made up of cancerous breast cells (not lung cells) and is then described as metastatic breast cancer (not lung cancer).
If it is not possible to identify the type of cancer cells the diagnosis is CUP.
In 2013, 2704 people in Australia were diagnosed with CUP.
In 2014, there were 2495 deaths in Australia due to CUP.
Some people with metastatic cancer have no symptoms, but common symptoms may include:
- breathlessness or discomfort in the chest
- bone pain, back pain
- swelling and discomfort in the abdomen, fluid collecting in the abdomen (ascites), yellowing of the skin and eyes (jaundice)
- swollen lymph glands such as those in the neck, underarm, chest or groin
- general symptoms such as weight loss, headaches, no appetite and feeling extremely tired.
For patients with CUP, the primary cancer site is not known, therefore it is difficult to identify risk factors. Smoking may be an important risk factor, as more than half of cancer of unknown primary patients have a history of smoking. Other risk factors may include older age, diet, alcohol and obesity – common risk factors for many cancers.
CUP is not diagnosed until a patient has metastatic cancer, and treatment is difficult because the primary cancer type cannot be determined.
Tests are ordered to ensure that cancers which are still curable or treatable, even when spread, are not missed.
Tests are done based on the site of the secondary cancer/s and any ‘clues’ as to where the cancer may have started. Tests can include:
These will examine the number and type of blood cells and measure the levels of certain blood chemicals (tumour markers).
Urine can be tested for any abnormal cells or to see if there are any problems with organs such as the kidneys or bladder.
Samples of tissue from a secondary tumour or an enlarged lymph gland are removed for examination under a microscope.
A procedure that uses an instrument called an endoscope to look inside the body and remove small tissue samples.
X-rays, ultrasounds and CT of the abdomen and pelvis, mammography, MRI and PET scans create pictures of the inside of the body.
A histopathogical review of all biopsy material using immunohistochemistry may also be undertaken.
If these tests find where the cancer started, the cancer is no longer an unknown primary and is treated according to the tissue of origin.
Staging differs for different cancer types. For most cancers there are four stages, with stage I being an early cancer and stage IV an advanced cancer.
Because a CUP has already spread, it must be stage II or higher. If it has spread to another body organ, it is a stage IV cancer.
Types of treatment
For most cancers, treatment is determined by the type of cancer and depends on correct diagnosis and staging. Because the primary cancer is unknown, there is no standard treatment for CUP.
The main treatment used for CUP is broad spectrum chemotherapy, unless the unknown primary is in a very specific area. For example, neck nodes are usually treated like head and neck cancer, axillary node presentations are treated in the same manner as breast cancers, and peritoneal presentations are treated like ovarian cancer.
In some cases of CUP, your medical team may talk to you about palliative care. Palliative care aims to improve your quality of life by alleviating symptoms of cancer.
As well as slowing the spread of CUP, palliative treatment can relieve pain and help manage other symptoms. Treatment may include radiotherapy, chemotherapy or other drug therapies
The health professionals you see will depend on the symptoms you have and the presumed location of the primary cancer. A few hospitals have dedicated CUP clinics. Your treatment team may include:
- GP who can help with treatment decisions and works with your specialists
- respiratory physician
- radiation oncologist
- radiation therapist
- medical oncologist
- cancer care coordinator
- palliative care doctors and nurses
- other allied health professionals, such as a psychologist and physiotherapist.
There is currently no screening for CUP available in Australia.
It is not possible for a doctor to predict the exact course of a disease, as it will depend on each person’s individual circumstances. However, your doctor may give you a prognosis – the likely outcome of the disease – based on the test results, the rate of tumour growth, as well as your age, fitness and medical history.
Although most cancers of unknown primary can’t be cured, treatment can keep some cancers of unknown primary under control for months or years.
Since the causes of CUP are unknown, there is no prevention advice specific to this disease. Having a generally healthy lifestyle – including not smoking, maintaining a healthy diet and weight and limiting alcohol consumption – may be protective.
Understanding Cancer of Unknown Primary, Cancer Council Australia, ©2016. Last medical review of this booklet: May 2016.
Australian Institute of Health and Welfare 2012. Cancer survival and prevalence in Australia: period estimates from 1982 to 2010. Cancer Series no. 69. Cat. no. CAN 65. Canberra: AIHW.
Australian Institute of Health and Welfare. ACIM (Australian Cancer Incidence and Mortality) Books. Canberra: AIHW.
Australian Institute of Health and Welfare (AIHW) 2017. Cancer in Australia 2017. Cancer series no. 101. Cat. no. CAN 100. Canberra: AIHW